Spray when it pays

For just a moment, compare your weed-control program to a boxing match. In one corner stands your tender corn crop. In another, tough weeds flex their muscles. If allowed to duke it out, your corn stands about as much chance as a 90-pound weakling does against Evander Holyfield.

Knowing that weeds always beat corn in the battle for nutrients, this scenario seems unlikely. Yet it's occurring in fields across the Corn Belt, say university weed extension specialists. The reasons: Commodity prices are low, resulting in cost-cutting measures; and farm size is increasing, so growers have more responsibility and less time than ever before to get the job done.

"With more acreage, farmers are looking for ways to simplify their weed-control programs," says Bob Hartzler, extension weed specialist at Iowa State University. "But in simplifying their weed control, they may be sacrificing performance."

As farms increase in size, corn growers struggle with the sheer number and diversity of tasks. They're also relying less on cultivation in order to minimize fuel costs and reduce wear and tear on ground and equipment. Considering current prices, farmers can build a good argument for a one-pass system. But inherently, it's risky. Spring weather can play havoc with the best of plans.

Comprehensive control. Farm-ers need a comprehensive weed-control strategy. Bill Lueschen, professor of agronomy at the University of Minnesota, says that growers should not rely on any single product or management approach. They should use both preemergence and postemergence products, says Steve Crosbie, regional biologist for BASF Corporation. The company markets what it calls the planned Frontier Two-Pass program in corn and soybeans, which combines this preemergence grass herbicide with any of several postemergence herbicides. The program allows growers to control grass and small-seeded broadleaves early on while analyzing their post weed-control needs.

Proper application. No-till farmer Ray Mc-Cormick understands the need for a strategic weed-control program. McCormick grows nearly 1,200 acres of white food-grade corn on southwest Indiana land that varies from gently rolling hills to flat flood plains bound by the White and Wabash Rivers. The plains are prone to problems, but McCormick is adamant. "Weeds," he says, "are not an option."

A combination of early preplant herbicides, postemergent spraying and a hands-on management style help him secure success. The preplant part of McCormick's weed-control program allows him to plant into a weed-free environment. Sometimes, in the February to April time frame, rain alters his plans. When that occurs, he goes into the field immediately after planting and applies a combination of burn down and an atrazine for a residual, according to flood proneness of the ground.

McCormick's post program varies, depending upon the weeds he identifies during scouting and their height and concentration from field to field. Most years he uses Accent for grass control and then Marksman or Clarity herbicides to knock out broadleaves. Last year he used Celebrity herbicide, which provides both grass and broadleaf control, instead of the Accent and Clarity and gained considerable savings. In addition, where the atrazine from his preplant program didn't appear to work as well because of excessive rainfall, he used Marksman to secure residual activity.

"This program attacks 100 percent of the weeds in my fields," he says. "It also packs a wallop on perennials which used to be my headache; they'd come back to haunt me in soybeans. Not anymore."

McCormick invests a total of $26 to $30/acre on his herbicide program. Of that, $6 goes to preplant applications, with the balance in post applications. "Never compromise your herbicide choices to cut herbicide costs when you're no-till farming," he admonishes. "Proper chemistry and proper applications are critical."

Early is best. Proper timing is also necessary. This means eliminating weeds early to allow the crop to reach its full yield potential. Lueschen encourages growers to target 4-in. and smaller weeds. When planting occurs around April 15 in Minnesota, he says, weeds need about four weeks to reach that 4-in. size. From there, because of a combination of heat, rain and simple exponential growth, weeds may require only five days to reach 8 in. The time required for weeds to reach 8 in. in states further south may be even less because of warmer soil temperatures.

The results achieved by controlling 4-in. vs. 8-in. weeds is significant. Research conducted between 1990 and 1994 at the University of Minnesota southern experiment station near Waseka confirms that fact. There Lueschen observed yield reductions of up to 35% when weeds such as giant foxtail, woolly cupgrass and wild proso millet reached 6 to 8 in. vs. just 3 to 4 in.

"These yield losses occurred even when we achieved 100 percent control at that larger size," Lueschen recalls.

That means that even if growers secure control of larger weeds, they're still sacrificing yield potential. Hartzler explains that damage from weeds is greatest with those weeds that compete with the crop the entire growing season. For instance, cocklebur infestations of 61 plants/100 ft. of row causes 3 to 19% yield loss. Lambsquarters, at the same infestation level, shows 0 to 8% loss. Velvetleaf, at one plant every 4 ft., results in a 25 to 45% yield loss.

With farmers adopting simplified weed-control programs, other problems are arising, says Hartzler. Waterhemp is an example of a weed that is increasing in prominence because of changes in weed-control programs. One reason for its rise is that it emerges later in the growing season than many other weeds, thus allowing it to escape many postemergence treatments. "We're seeing weeds emerge after the residual is gone," Hartzler says. "They initially cause minimal yield loss, but they produce considerable seed that impacts the following year."

Know the hot spots. The potential for future problems is one more reason farmers need to develop a diversified weed-control strategy and vary it depending upon their needs from year to year. Such an approach includes scouting and mapping fields.

Lueschen advises farmers to walk fields and monitor weed pressure weekly until weeds are under control. For the best weed-monitoring results, he says, corn growers should walk each of their fields using a Z-pattern approach. That's the method that professional consultants typically use, and it works well.

Hartzler encourages farmers to check known hot spots for weeds because fields rarely have uniform weed problems. "Say on 160 acres you only have 20 acres of severe problems with woolly cupgrass," he says. "Spray a broad-base herbicide on the 160 and then do the specific job that's needed on the woolly cupgrass."

He adds that new technology is making this approach more feasible. Variable rate application abilities enable corn producers to program their sprayers to accomplish this goal.

Crosbie says he sees farmers and custom applicators applying post herbicides later than the optimal time. "Here, farmers go from corn planting right into soybean planting, and the time crunch will get them," he says. He encourages corn producers to maintain a sprayer, which offers additional flexibility and can make a significant contribution to weed control once timing is critical.Safety features. Lueschen offers suggestions, which he calls safety features, for farmers to consider this year:

Know your weeds in every field so you can develop a program suited to your needs.

Use both pre- and post-applied products. This is the best risk-benefit management approach.

Consider cultivation. Used judiciously, it's still a good fit for conventional operators.

Consider banding herbicides rather than broad-based applications.Get the jump on weeds early to give your corn crop the best opportunity to reach its full yield potential.